The present invention relates to a system separating filter for separating two signals wherein each includes a doubly polarized frequency band with the two bands being at different frequencies. More particularly, the present invention relates to such a filter which includes a first waveguide section in which both frequency bands exist with their respective double polarizations, a second waveguide section which serves as a transition piece and a third waveguide section.
The construction of highly intertwined radio communication-links and the local conditions of limited space on the antenna platforms of radio towers make it seem desirable to utilize broadband antennas in at least two frequency bands with two polarizations. Particularly favorable is a broadband antenna (e.g. a parabolic horn, a Cassegrain antenna or a parabolic reflector antenna) with offset feed in conjunction with an appropriately designed separating filter. Such filters have previously usually been designed with selective 0 dB couplers, the main drawbacks of which are their great structural length, their coupling losses and the excitation of higher, undesired wave modes.